[BUG] The pass "eliminate_nop_cast" causes output mismatch

[BUG] The pass "eliminate_nop_cast" causes output mismatch

Issue
Running the single pass eliminate_nop_cast with onnxoptimizer 0.4.2 changes numerical outputs.ORT graph optimizations are disabled during differential testing.

Environment

• Ubuntu20.04
• Python 3.10
• onnx==1.19.0
• onnxruntime==1.23.2
• onnxoptimizer==0.4.2 (latest)

Repro steps (run from this folder)

1. Create a Python environment (Python 3.10) and install dependencies:

python3 -m venv .venv
source .venv/bin/activate
pip install -U pip
pip install -r requirements.txt

2. Optimize a case with only eliminate_nop_cast (writes model.opt.onnx next to model.onnx):

• python optimize_model.py --case ./case_04319_seed54453180
• python optimize_model.py --case ./case_06878_seed74717901

1. Differential test for original and optimized models with same oracle inputs:

• python diff_test.py --case ./case_04319_seed54453180
• python diff_test.py --case ./case_06878_seed74717901

Observed results
Mismatches appear in the two cases abouve.

Expected
eliminate_nop_cast should be semantics-preserving. Applying this pass alone should not change any output values.

Differential Test Output Details

1. case_04319_seed54453180 — output[6] max_abs=3.174e-01 max_rel=1.693e-01; output[8] max_abs=4.484e+18 max_rel=4.484e+26; overall mismatch.
2. case_06878_seed74717901 — output[4] max_abs=6.900e+01 max_rel=5.694e+01 (largest); output[1] max_abs=7.354e+00 max_rel=1.316e+00; overall mismatch.

Case: case_04319_seed54453180 (ORT graph optimizations disabled)
  output[0]: max_abs=0.000e+00, max_rel=0.000e+00, shape=(9, 1)
  output[1]: max_abs=0.000e+00, max_rel=0.000e+00, shape=(1, 53)
  output[2]: max_abs=0.000e+00, max_rel=0.000e+00, shape=(9, 53)
  output[3]: max_abs=0.000e+00, max_rel=0.000e+00, shape=(9, 53)
  output[4]: max_abs=0.000e+00, max_rel=0.000e+00, shape=(9, 53)
  output[5]: max_abs=0.000e+00, max_rel=0.000e+00, shape=(9, 53)
  output[6]: max_abs=3.174e-01, max_rel=1.693e-01, shape=(9, 53)
  output[7]: max_abs=0.000e+00, max_rel=0.000e+00, shape=(53, 9)
  output[8]: max_abs=4.484e+18, max_rel=4.484e+26, shape=(1, 1, 1)
  output[9]: max_abs=0.000e+00, max_rel=0.000e+00, shape=(9,)
  output[10]: max_abs=0.000e+00, max_rel=0.000e+00, shape=(9, 53)
  output[11]: max_abs=0.000e+00, max_rel=0.000e+00, shape=(9, 53)
  output[12]: max_abs=0.000e+00, max_rel=0.000e+00, shape=(9, 53)
  output[13]: max_abs=0.000e+00, max_rel=0.000e+00, shape=(9, 53)
  output[14]: max_abs=0.000e+00, max_rel=0.000e+00, shape=(9, 53)
Overall: max_abs=4.484e+18, max_rel=4.484e+26
Case: case_06878_seed74717901 (ORT graph optimizations disabled)
  output[0]: max_abs=0.000e+00, max_rel=0.000e+00, shape=(46, 47)
  output[1]: max_abs=7.354e+00, max_rel=1.316e+00, shape=(47, 47)
  output[2]: max_abs=0.000e+00, max_rel=0.000e+00, shape=(47, 47)
  output[3]: max_abs=0.000e+00, max_rel=0.000e+00, shape=(47,)
  output[4]: max_abs=6.900e+01, max_rel=5.694e+01, shape=(1, 47, 49)
  output[5]: max_abs=0.000e+00, max_rel=0.000e+00, shape=(1, 47, 1)
  output[6]: max_abs=0.000e+00, max_rel=0.000e+00, shape=(47,)
  output[7]: max_abs=0.000e+00, max_rel=0.000e+00, shape=()
  output[8]: max_abs=0.000e+00, max_rel=0.000e+00, shape=(47, 47)
Overall: max_abs=6.900e+01, max_rel=5.694e+01

Attachments

• requirements.txt
• optimize_model.py
• diff_test.py (runs original and optimized with same oracle inputs; ORT graph optimizations disabled)
• run_optimized_model.py (executes optimized model with oracle inputs)
• case_04319_seed54453180/ (original and optimized model with oracle inputs)
• case_06878_seed74717901/ (original and optimized model with oracle inputs)

Run optimize_model.py and diff_test.py for case_04319_seed54453180 and case_06878_seed74717901 using the supplied requirements.txt, with ORT graph optimizations disabled. Inspect the eliminate_nop_cast pass entry point and compare the original and optimized outputs; done means both cases produce identical outputs when that pass is applied alone.